초록

The efflux of 45Ca 2+ from preloaded intracellular stores of saponin-permeabilised human uterine artery smooth muscle cultured cells was used to study the mechanisms underlying Ca 2+ release from the sarcoplasmic reticulum (SR). The present paper demonstrates directly a functional Ca 2+ release mechanism that is dependent on an increase in free Ca 2+ (100 nM-30 μM) and is completely inhibited by 20 μM Ruthenium red. The amount of Ca 2+ released at 30 μM free Ca 2+ was reduced by approximately 50% compared to the release at 10 μM. This Ca 2+-induced Ca 2+ release (CICR) mechanism was not sensitive to caffeine. Exposure of cells to low free Ca 2+-containing solutions (10 nM) indicated that a component of the CICR mechanism may be functional at basal free Ca 2+ levels of 100 nM. Application of ryanodine (0.1–100 μM) induced 45Ca 2+ efflux from the sarcoplasmic reticulum and this release was also inhibited by 20 μM Ruthenium red.